Safety control system for air heater



A. H. ROBSON 3,051,227

Aug. 28, 1962 I SAFETY CONTROL SYSTEM FOR AIR HEATER 2 Sheets-Sheet 1 Filed Feb. 23, 1960 MAGNETO 66 J/G.

68D I (3 Pressure Conirolled I Valve 8 26 f A r 28 REG I68 @MAGNETO I04 I62 I r gig- 7402 /|88 $22 (I92 $194 |s4 INVENTOR. FR AUBREY H. ROBSON BY M44 M f ATTORN EY Aug. 28, 1962 A. H. ROBSON 3,051,227

SAFETY CONTROL SYSTEM FOR AIR HEATER Filed Feb. 23, 1960 2 Sheets-Sheet 2 PRESSURE CONTROLLED J 1 v v INVENTOR. AUBREY H. ROBSON BY M6. Q y

ATTORNEY o l i it 3,051,227 SAFETY CONTROL SYEBTEM FOR HEATER Aubrey H. Robson, Rock Island, 111., assignor to American Air Filter Company, Inc, Louisvilie, Ky., a corporation of Delaware Filed Feb. 23, 196i}, Ser. No. 10,188 Claims. (Cl. 158-28) This invention relates to a control system for a portable air heater of the type having a burner bypass fuel control system.

One object of the present invention is to provide, in such a fuel control system, combustion condition safety control including reset demand means to prevent recycling of the heater after shutdown resulting from operation of such safety control.

Another object is to provide a control system which, within the limits of the relatively simple and inexpensive control elements of the system is arranged to quickly terminate fuel flow to the burner in response to failure of safety conditions.

Another object is to provide a control system responsive in part to fuel pressure conditions indicative of fuel flow to the burner.

Additional objects of the invention will be appreciated from the following description taken in connection with the accompanying drawing illustrating several embodiments incorporating the principles of the invention by way of example, and wherein:

FIGURE 1 is a digrammatic view of one form of the invention;

FIGURE 2 is a diagrammatic view of a modified form of the invention;

FIGURE 3 is a fragmentary diagrammatic View of a modification of FIGURE 1; and,

FIGURE 4 is another fragmentary diagrammatic view of a modification of FIGURE 1.

A heater and fuel system of the general type adapted for utilizing the principles of the present invention is disclosed in Hubbard US. Patent 2,758,591. Broadly speaking such a fuel system includes, among other things: a source of fuel; a fuel pump which delivers fuel to a line containing a pressure regulating valve adapted to open in response to received fuel of a least a given pressure and to pass fuel into a nozzle supply line; a jet type fuel discharge nozzle connected to receive fuel from the nozzle supply line and discharge a part of it into the burner; a thermostatic valve which controls the rate at which fuel is discharged into the burner by throttling a nozzle return line in accordance with the temperature of the ventilating air discharged from the heater; and a normally open primary bypass valve in a fuel line connected between the pump and the regulating valve, and operable when open to return the fuel pump output back to the fuel source so that the regulating valve remains closed and fuel flow to the nozzle is terminated or prevented.

In carrying out the present invention, as applied to such a system, an additional bypass valve in parallel with the noted primary bypass valve is provided, this additional bypass valve being normally closed and operable to an open position by energization of an associated solenoid in response to combustion failure. The control circuit for the solenoid includes a normally closed combustion responsive or stack switch which opens in a predetermined time in response to heat of combustion and remains open thereafter so long as combustion continues, and a normally open time delay switch operative to a closed position in a time period exceeding the time required for opening the stack switch under normal heater firing conditions so that the stack switch can open before the time delay switch closes. The time delay switch is controlled by an electrically powered element such as a resistance heater initially energized simultaneously with fuel flow beginning to the burner, this being accomplished by closing a fuel pressure responsive switch responsive to the fuel pressure in the fuel lines interconnecting the fuel pump, the regulating valve, and the two paralnypass valves Referring to FIGURE 1, a source of liquid fuel such as gasoline in tank 2 is forced by pump 4 into a fuel line a interconnecting the pump and a pressure regulating valve 8. Both a first fuel bypass line 16 containing bypass valve 12, and a second and parallel bypass line 14 containing bypass valve 16 are connected to fuel line 6. The first bypass valve 12 is controlled by solenoid 18 and is biased to a closed position except when solenoid is is energized. The bypass valve 16 is a normally open valve which is closed by manually depressing knob 20, and which remains closed so long as the fuel pressure in the bypass line 14 exceeds a predetermined minimum fuel pressure indicative of regulating valve '8 being open.

In addition to valve 16 serving as a combustion start valve, it also serves as a ventilating air overheat safety valve. To this end, a temperature sensing element 22 suitably located in the heated ventilating air stream at the heater outlet is adapted to cause valve 16 to open in the event the ventilating air temperature exceeds a selected temperature.

A secondary bypass line 24 connected to the regulating valve 8 serves to return to the tank 2 such fuel as is not required to maintain a predetermined pressure in the nozzle supply line 26.

A jet type nozzle 28 having a built-in by-pass receives fuel from nozzle supply line 26 and discharges part of it into the burner (not shown) and passes the remainder of the fuel received into the nozzle return line 30. The nozzle return line 30 contains a thermally controlled valve which serves to throttle the nozzle return line in accordance with the diiferential between a selected ven tilating air temperature to which the valve is adjusted and the ventilating air temperature sensed by thermostatic element '34 also suitably located in the ventilating air stream emerging from the heater. Any fuel bypassed through lines 10, 14 or 24, or passing through valve 32 is returned to the fuel tank 2.

With the exception of the first bypass line 10, valve 12 and solenoid 18, details of the structure and operational characteristics of each of the enumerated elements may be derived from the noted Hubbard patent.

The electrical control circuit for the FIGURE 1 system includes a first circuit having a normally closed combustion responsive or stack switch 36 suitably located in the exhaust gas stack of the heater and operable to an open position in a predetermined time in response to heat generated by combustion in the burner, an electrical line 38 series connecting the stack switch and a conventional normally open time delay switch 40 such as a heated warp bar adapted to be moved to a closed position after expiration of a selected time period causing the opening of stack switch 36 if combustion has been initiated, a line 42 connecting the time delay switch 40 to one side of the solenoid 18, and another electrical line 44 connecting the other side of the solenoid 18 to a source of electrical power.

A second circuit shown in parallel with the first circuit includes a fuel pressure responsive switch 46 which is normally open and closes in response to a predetermined pressure in the fuel line 6 indicating fuel flow to the burner, and an electrical line 48 series connecting switch 46 to a resistance heating element St} physically adjacent the time delay switch 40 so that the heat emitted by the energized element 50 will, in the selected time period,

3 cause switch to close and remain closed so long as heating element is energized. While element 50 may be connected to line 38 rather than directly to the ground so that the element 50 will not be constantly energized during normal heater operation, it will be appreciated that upon a combustion failure that switch 36 must first close'before element 50 can be energized to cause closure of switch 40, thus prolonging the period between the combustion failure and resultant bypassing of fuel.

The source of electrical power may conveniently be a generator 58 delivering power through a conventional current sensitive relay 6%). The generator is driven by a prime mover (not shown) such as an internal combustion engine or an electric motor which serves to furnish the ventilating air and, if so arranged, the combustion air for the heater.

An electric line 62 connects the source of power through switch 64 to an accessory drive electric motor 66 which drives the fuel pump 4 and an ignition magneto 68. It will be noted that since power is not available to accessory drive motor 66 until the prime mover reaches normal operating speed, that ignition in the burner cannot take place until some combustion air has scavenged the burner.

For purposes of explanation of the operation of the apparatus of FIGURE 1, it will be assumed that an internal combustion engine prime mover is used and that the heater is being started after a period of normal shut-down. Before starting the heater, valve 12 will be closed, valve 16 will be open, valve 8 will be closed, and valve 32 will have been set for controlling fuel discharge into the burner to obtain a selected ventilating air temperature. When the internal combustion engine reaches normal operating speed, power will be available through the current sensitive relay 60. Switch 64 is then closed manually to energize the accessory drive motor 66 which drives the pump 4 and magneto 68. Since valve 16 is open, thereby preventing a build up in fuel presure suflicient to open regulating valve 8, the full pump output will bypass back to the tank through bypass line 14. Both solenoid 18 and heating element 511 are de-energized due to time delay switch 40 and fuel pressure responsive switch 46 respectively being open. When it is desired to initiate combustion, knob'20 is actuated to close valve 16. With both bypass valves 12 and 16 closed, the fuel pressure in line '6 will rapidly build up sufficiently to open valve 8 and permit fuel flow .to the nozzle through nozzle supply line 26. Ignition will take place due to magneto 63 having previously been placed in operation. When the pressure in line 6 causes valve 8 to open, the fuel pressure responsive element 7 0, which is selected to close switch 46 at this predetermined pressure, will close switch 46 and thus energize the resistance heating element 54 in the delay relay.

When the stack temperature reaches a predetermined minimum the stack switch 36 opens. This switch may be a snap actuation bi-metallic element selected to open in a predetermined time in response to heat generated by normal combustion initiation. The time delay switch 40 is selected so that it will close in response to the heat emitted from resistance heater element 50 in a time which exceeds the time it takes the stack switch 36 to open. Thus, under heater start-up conditions normally encountered, the stack switch 36 will open slightly before the time delay switch 40 closes, so that the solenoid 18 will remain de-energized and the associated valve 12 will remain in its normally closed position. If combustion is not initiated in the burner the stack switch 36 will of course remain closed. Then when the time delay switch 49 closes in response to heat from energized heater ele ment 50, the solenoid 18 will be energized and bypass valve 12 will open. Thus fuel flow to the nozzle will be terminated by closure of regulating valve 8 in response to loss of fuel pressure in line 6.

If a flame failure occurs during normal heater operation, cooling and resultant closure of stack switch 36 will 4, complete the first circuit and cause valve 12 to open and bypass fuel. It will be appreciated that when fuel pressure in line 6 is reduced by opening of either bypass valve 12 or 16, the fuel pressure responsive switch 46 will be opened and remain open so that the second circuit is opened and resistance heater St) de-energized permitting time delay switch 441 to cool and resume its open position.

Since valve 16 is maintained in its closed position by fuel pressure in line 6 after valve '16 has been initially closed by knob 29, if valve 12 opens because of fiameout or ignition failure, the valve 16 will also open. If a ventilating air overheat occurs, valve 16 will also be opened in response thereto. Thus, after heater shutdown due to any safety condition failure, before heater operation can again be initiated, the knob 21 must be manually operated to close valve 16. This arrangement serves to provide the reset demand for the heater and prevents the heater from recycling after any safety failure. Since termination of fuel flow to the burner as a result of safety shutdown does not automatically terminate combustion air flow, the burner is purged or scavenged.

With the arrangement thus far described, after a safety shutdown the heater is automatically in a condition for resuming combustion by closing valve 16. Under certain circumstances it may be desirable to command more forcibly the operators attention after safety shutdown. As shown in FIGURE 3, by omitting the fuel pressure responsive element 71) and its associated switch 46, and connecting line 44 to line 48 by the normally closed switch 52, it will be appreciated that after heater failure this reset demand switch 52 must be manually held open for a sufiiciently long time to permit switch 40 to cool and open. However, it will also be appreciated that such an arrangement imposes the disadvantage that upon starting combustion the switch 52 must be held open until knob 20 is operated to close valve 16.

Referring again to FIGURE 1, it is noted that with the electrical connection between the solenoid 18 and power source as shown (i.e., line 44 directly connecting the solenoid to the power source), that when flameout or ignition failure occurs and time delay switch 40 closes, the valve 12 controlled by solenoid 18 will remain in an open position until switch 46 opens after cooling. It will be appreciated that the solenoid 18 can be connected to the power source through pressure responsive switch 46 rather than being directly connected. With such an arrangement, as is shown in FIGURE 4, wherein line 43 connects one side of solenoid 18 to line 48, in the event of an ignition failure or flameout, the valve 12 will re main open only until the drop in fuel pressure in line 6 causes switch 46 to open. Restarting of combustion must await cooling of switch 40 however.

Referring now to FIGURE 2 wherein another modified form of the invention is shown, those elements in FIG- URE 2 which are the same as the elements in FIG- URE l are designated by the same numerals as in FIG- URE 1 raised by 100. In FIGURE 2, the burner start valve and overheat valve designated 16 in FIGURE 1 is replaced by a normally open valve 172 controlled by solenoid 174.

A momentary closure start switch 176 is connected to the power line 144, and byline 180 to a push-.to-open stop switch 182 and a reset relay winding 184 which closes relay actuated switch 186 upon energization of the winding. One side of relay switch 186 is connetced to the power line 144 while the other side is connected by line 188 to the solenoid 174 controlling valve 172. The solenoid circuit is completed by line 190, a normally closed ventilating air overheat switch 192, and a normally open combustion air presseure responsive switch 194. One side of stop switch 182 is connected to line 148 which is also connected to: one side of fuel pressure responsive switch 146, one side of solenoid 118 controlling valve 112 and one side of resistance heating element As was noted in connection with the comparison between the FIGURE 1 and FIGURE 4 arrangements, solenoid 118 can be connected directly to the power line 144 instead of being connected to the power line through fuel pressure responsive switch 146.

In operating the system of FIGURE 2, after ventilation and combustion air flow are established switch 164 is closed to initiate operation of the accessory drive motor 166 driving fuel pump 104 and magneto 168. Under these conditions, since valve 172 is open, fuel is bypassed back to the tank and regulating valve 168 remains closed. When it is desired to initiate combustion, start switch 176 is momentarily closed, thereby energizing relay winding 184 and causing closure of its associated switch 186. When switch 186 closes, solenoid 174 is energized since ventilating air overheat switch 192 is in its normally closed position and switch 194, closed by combustion air pressure completes the circuit. Thus bypass valve 172 is closed and fuel pressure builds up sufficiently in line 166 to open regulating valve 198 and pass fuel to the jet nozd zle 128 where it is ignited. The fuel pressure in line 106 closes fuel pressure responsive switch 146 and completes the circuit from the power line 144 through switch 146, line 148, normally closed stop switch 182 and line 180 to the relay winding 184 which remains energized and holds switch 186 closed. Thus solenoid 174 remains en ergized and consequently maintains bypass valve 172 closed.

When switch 146 closes, the resistance heating element 150 is also energized and begins to heat time delay switch 140. If combustion is not established, stack switch 136 will remain closed and when time delay switch 140 closes, the bypass valve 112 will be opened by energization of its associated solenoid 118. Similarly, if combustion has been established and a flameout subsequently occurs, bypass valve 112 will open. If either bypass valve 112 or 172 opens, the fuel pressure in line 106 quickly drops to a degree which causes regulating valve 108 to close and switch 146 opens. Thus reset relay winding 184 is de-energized and its associated switch 186 opens, thereby de-energizing solenoid 174 and causing bypass valve 172 to assume its normally open position. Resistance heater element 150 is simultaneously de-energized by opening of fuel pressure responsive siwtch 146 and consequently the time delay switch 140 will cool and open.

If overheating of the ventilating air occurs, the overheat switch 192 opens and de-energizes solenoid 174 so that bypass valve 172 opens. In this case the same reduction in fuel pressure in fuel line 106 causes switch 146 to be opened, thereby de-enerigizing both reset relay winding 184 and resistance heater element 150 so that all elements will be in a condition for normal re-starting of the heater when desired. As will be appreciated, momentary opening of stop switch 182 will similarly cause heater shutdown through opening of switch 186.

It will be noted that with the systems of both FIG- URES 1 and 2, that burner combustion termination for any reason places the system in a condition where it cannot be automatically restarted but requires the attention of an operator to restart burner combustion. At the same time the elements cooperate with each other in such a manner that when a burner shutdown occurs through functioning of safety apparatus, the elements are automatically returned to a position permitting a normal combustion start.

The invention claimed is:

1. In a bypass type fuel control system for an air heater having a liquid fuel burner: fuel line means; means for supplying fuel under pressure to said fuel line means; a normally closed fuel pressure regulating valve in said fuel line means operable to open and pass fuel to said burner in response to a predetermined fuel pressure in said fuel line means; a first fuel bypass line connected to said fuel line means; -a second fuel bypass line connected to said fuel line means; a normally closed first bypass valve in said first bypass line; a solenoid for operating said first bypass valve to an open position upon energization thereof; a normally open second bypass valve in said second bypass line operable in a closed position to initiate fuel flow to said burner by increasing the fuel pressure in said fuel line means to at least said predetermined fuel pressure; a source of electrical power; time delay switch means includin a normally open time delay switch and an electrically energized Operator operable in response to energization thereof to close said time delay switch at the end of a first predetermined time period; a normally closed combustion responsive switch operable to an open position during a second maximum predetermined time period less than said first predetermined time period in response to initiation of combustion in said burner; a first circuit including said solenoid, said time delay switch, and said combustion responsive switch connected in series; a second circuit including said operator in parallel with said first circuit; means including a normally open fuel pressure responsive switch operable to a closed position in response to a fuel pressure in said fuel line means corresponding to said regulating valve being open, said pressure responsive switch being connected between said power source and said time delay switch operator so that said operator is only energized while said regulating valve is open and fuel is flowing to said burner.

2. The system of claim 1 wherein: said first circuit is connected to said power source through said pressure responsive switch.

3. The system of claim 1 wherein: a second solenoid is provided for actuating said second bypass valve to a closed position upon energization of said second solenoid; relay means including a normally open switch and a winding operable in response to energization thereof to close said switch; a third circuit is provided including said second solenoid and said relay switch connecting said third circuit to said power source; a fourth circuit is provided including said relay winding for actuating said relay switch when energized and a normally open start switch connected to said source of power; and a fifth circuit is provided con necting said relay winding to said pressure responsive switch whereby energization of said relay winding after starting fuel flow to said burner is dependent upon said regulating valve remaining open.

4. The system of claim 3 including: normally closed switch means in said third circuit operable to an open position to de-energize said second solenoid in response to an overheat condition of said heater produced by said burner.

5. In a bypass type fuel control system for an air heater having a liquid fuel burner: a source of fuel; a fuel pump; a fuel pressure regulating valve adapted to open and pass fuel to said burner in response to receiving fuel of a predetermined pressure; fuel line means interconnecting said pump and said regulating valve; a first fuel bypass line including a first normally closed bypass valve connected to said fuel line means and operative in an open position to return fuel to said source; a second fuel bypass line in parallel with said first bypass line including a second normally open bypass valve connected to said fuel line means; an electrical power source; means for closing said second bypass valve to initiate fuel flow to said burner; first circuit means for controlling said first bypass valve including, in series, a solenoid operable to open said valve when energized, a normally open time delay switch, and a normally closed combustion responsive switch operable to an open position during a maximum predetermined time in response to initiation of combustion in said burner; second circuit means for controlling said time delay switch including electrically powered means operable, when energized, to close said time delay switch in a second predetermined time exceeding said maximum predetermined time; and, means including a normally open fuel pressure responsive switch operable to a closed position to energize said second circuit means in response to a fuel pressure condition corresponding to fuel fiow to said burner. 6. In an air heater of the type wherein fuel flow to a burner is controlled by bypassing fuel around said burner, a fuel control system comprising: a first fuel bypass line including a first normally open bypass fuel valve adapted to be manually operated to a closed position, and to be maintained in said closed position by fuel pressure exceeding a predetermined minimum at the inlet to said valve; a second fuel bypass line including a normally closed second bypass fuel valve; a solenoid operable to open said second valve upon energization thereof; an electrical power source; time delay switch means including a normally open time delay switch and an electrically energized operator operable in response to energization thereof to close said time delay switch at the end of a first selected time; first circuit means connected to said power source and including, in series, said solenoid, said time delay switch and a normally closed combustion responsive switch operable to an open position during a maximum predetermined time less than said selected time in response to initiation of combustion in said burner; means including a normally open fuel pressure responsive switch operable to a closedposition in response to a fuel pressure corresponding to fuel flow to said burner; and second circuit means including said operator, and said fuel pressure responsive switch connected to said power source.

'7. In a fuel control system of the 'burner bypass type: a burner bypass fuel line; a solenoid; a normally closed valve in said bypass line operable to an open position upon energization of said solenoid to prevent fuel flow to said burner; time delay switch means including a nor mally open time delay switch and an electrically energized operator operable in response to energization thereof to close said time delay switch at the end of a first predetermined time; an electrical control circuit including said solenoid connected in series with said time delay switch and a normally closed combustion responsive switch operable to an open position during a maximum predetermined time period less than said first predetermined time period in response to heat generated by initiating combustion; and means including a normally open fuel pressure responsive switch connected to a source of power and operable to a closed position to energize said time de- 8 lay switch operator in response to a predetermined fuel pressure indicative of fuel flow to said burner.

8. In a bypass type fuel control system for a liquid fuel burner: a fuel pump; fuel supply line means connecting said pump and said burner; fuel bypass line means including a pair of bypass lines connected to return fuel from said supply line means; a first normally open valve in one of said bypass lines; a second normally closed valve in the other of said bypass lines; manually operated means for initially effecting closure of said first valve; means responsive to fuel pressure in said fuel supply line means for maintaining said first valve closed; an electrical power source; a solenoid operable to open said second valve when energized; time delay switch means including a normally open time delay switch and an electrically energized opera-tor operable in response to energization thereof to close said time delay switch at the end of a first predetermined time period; a normally closed combustion responsive switch operable to an open position during a second maximum predetermined time period less than said first predetermined time period in response to combustion in said burner; switch means operable in a closed position to energize said time delay switch operator; first circuit means including said solenoid, said time delay switch and said combustion responsive switch connected in series to said source of power; and second circuit means including said operator and said operator energizing switch means in series with said source of power.

9. The control system of claim 8 wherein; said energizing switch means for said time delay switch operator is biased to a normally closed position and is adapted to be manually operated to a momentary open position.

10. The control system of claim 8 wherein: said operator energizing switch means is a normally open switch; and means responsive to a fuel pressure in said fuel supply line means corresponding to fuel flow to said burner is provided to actuate said operator energizing switch means to a closed position.

References fitted in the file of this patent UNITED STATES PATENTS 

